Determination of layered nickel hydroxide phases in materials disordered by stacking faults and interstratification

Abstract

The formation of stacking faults and phase interstratification disorder in layered nickel(II) hydroxides during the chemical precipitation synthesis of materials using nickel(II) nitrate and potassium hydroxide solutions has been investigated in the temperature range of 5 °C to 95 °C and time intervals from 1 hour to 1 week. Stacking faulted materials were identified by broadening of the 00l reflections, while interstratified materials were identified through the splitting of the 001 into two lines. In contrast to the disorder concepts presented in previous studies of these materials, this work has shown through vibrational spectroscopy that both the alpha-phase and beta-phase hydroxides are present in materials described with stacking fault disorder, while layered hydroxysalts were additionally present in the materials considered to be interstratified. Standard mixtures of Ni₃(OH)₄(NO₃)₂ and β-Ni(OH)₂ were prepared to investigate if the intensity of particular vibrational bands could be correlated with the proportion of the particular phases in mixtures. The intensities of the C_2v nitrate infrared and Raman bands at 990 cm⁻¹ and 1315 cm⁻¹ were shown to correlate with the amount of layered hydroxynitrate incorporated in the phase, theoretically providing a method to determine the components in mixed compositions. Since disorder and phase impurities in layered nickel hydroxide materials affect both their electroactive stability and performance as cathode materials, this work has important implications in several research fields.